Stabilization of plasma generators

ABSTRACT

A LIQUID STABILIZED PLASMA GEMERATOR HAS A PATH OF FLOW FOR THE ARC DIVIDED INTO SECTIONS WITH THE FLOW CHANNEL CONSTRICTED AT THE TRANSITIONS BETWEEN THE SECTIONS, THE STABILIZING LIQUID BEING DIVIDED IN EACH SECTION INTO PARTIAL STREAMS ONE OF WHICH IS DISCHARGED FROM ITS SECTION IN THE VICINITY OF THE RESPECTIVE CONSTRUCTOR THROUGH A NARROW GAP EXTENDING NEAR THE INNER SURFACE OF THE LIQUID VORTEX. VARIOUS ARRANGEMENTS OF DIVISIONS ARE PROVIDED.

a awn XR 397129996 Jan. 23, 1973 KUGLER 3,712,996

STABILIZATFEON OF PLASMA GENERATORS Filed Feb. 24, 1972 3 Sheets-Sheet 1 Jan. 23, 1973 T. KUGLER 3,712,996

STABILIZATION OF PLASMA GENERATORS Filed Feb. 24, 1972 3 Sheets-Sheet 3 Fig.5

' Jan. 23, 1973 T. KUGLER STABILIZATION OF PLASMA GENERATORS 3 Sheets-Sheet 3 Filed Feb. 24, 1972 United States Patent SiTAlEllLlZATlON @F PLASMA GENERATURS Tiber Kugler, Sins, Switzerland, assignor to Lonza Ltd, Basel, Switzerland Continuation-impart of abandoned application Ser. No.

43,014, June 3, 11.970. This application Feb. 2d, 1972, Ser. No. 228,880 Claims priority, application gvitzerland, June Ill, 1969, 9 int. Cl. Htlh 31/26 lU.S. Cl. 313-2;3ll 3 Claims ABSTRACT 0F THE .UllSCLUdURE A liquid stabilized plasma generator has a path of flow for the are divided into sections with the flow channel constricted at the transitions between the sections, the stabilizing liquid being divided in each section into partial streams one of which is discharged from its section in the vicinity of the respective constrictor through a narrow gap extending near the inner surface of the liquid vortex. Various arrangements of divisions are provided.

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This is a continuation-in-part of Ser. No. 43,014, filed June 3, 1970, now abandoned.

The present invention relates to a method of, and a device for, the stabilization of an electric are burning in the interior of an elongate liquid vortex, in which the path of flow of the liquid is divided along the arc column into section and the flow channel is constricted at the transition from one section to another, and in which the liquid flow is kept erect by the supply of liquid at each of the sections of the flow path.

Liquid stabilized plasma generators are known in which the column of an arc discharge is kept erect in the channel of a liquid vortex, and the electrodes are arranged in at least one electrode chamber. The electrode chamber or each electrode chamber has outlets for discharging superfluous stabilizing liquid and also gas, steam and any products from the electrodes.

It is also known to divide the stabilizing channel in the axial direction by restrictors to enable operation of the plazma generator with a substantially smaller channel diameter than those of the electrodes and the electrode chambers. The restrictors have central openings of equal diameter, and between the restrictors tangential inlets for the input of stabilizing liquid are provided in the walls surrounding the channel. The liquid supplied is led off in a radial direction over the outer surfaces of the end restrictor and removed from the chamber. This construction enables satisfactory operation with substantially longer channels and higher powers than the previously used stabilization channels, which were made without axial divi sion or channels from tubes which were Wetted by a thin layer of rotating liquid, or of channels with porous walls through which the liquid was supplied to the inner surfaces of the channels.

Experiments have shown that it is possible with these prior plasma generators to reach powers of 250 kilowatts with a current of 50 amps and a voltage of 50 volts at the electrodes in continuous operation. If the power is increased by raising the voltage and the current is kept low, in order to obtain a low wearing of the electrodes, then substantially longer stabilizing channels must be employed than in the prior plasma generators. If the channels in the prior art plasma generators are extended, then in the currentless condition there is produced a narrowing of the free channel diameter and at a limit length, which is indirectly proportional to the diameter of the end restrictor in the stabilizing channel, the liquid-free space in the midiifilzfi b Patented titan. 23, 19731 dle of the channel disappears. In a stabilization channel in which the diameter of the free channel varies by an amount of more than one millimeter with an end restrictor having an opening diameter less than 8 millimeters, experiments have shown that a stably burning arc cannot be maintained. The plasma beam pulls liquid drops from the surfaces and these cause both a large fluctuation in the flow and in the voltage of the discharge and also a considerable reduction of temperature. When the free channel in the middle disappears, it is even impossible to produce the arc discharge.

It is an object of the present invention to mitigate the disadvantages of the known methods and plasma generators.

According to the present invention, the liquid supplied is divided in each of the sections into at least two partial streams and only one of the partial streams of the liquid is discharged from the respective sections in the vicinity of the respective constriction through a narrow space which extends to the vicinity of the inner surface of the liquid vortex.

By the method according to the invention it is also possible to supply different stabilizing liquids separately, e.g. into two separate chambers. It is also possible to feed in gases and/ or steam in addition to the stabilizing liquid. The gases and/ or steam can be fed through together with the liquid, e.g. under pressure, or separately. In the latter case it is advantageous to employ a restrictor extending into the arc zone beyond the inner diameter of the stabilizing liquid. This restrictor has the further advantage that by it the liquid in the channel can also be separated so that it can be drawn 01f separately at opposite sides and without mixing. In this way it is possible to draw 01f the electrode burning products near the electrodes with the liquid and thus to avoid contamination of the plasma ray.

The device for carrying out the method according to the invention comprises a stabilizing channel divided in the axial direction by divisions and has at least at one of the divisions a discharge space formed by a restrictor and said division, the diameter of the central opening of the restrictor being greater than the diameter of the opening of the divisions and smaller than the outer diameter of the stabilizing channel, at least one supply duct and a discharge duct, which is connected with the discharge space, being provided between the divisions.

Advantageously, the diameter of the central opening of the restrictor is at least 2 mm. larger than the diameter of the central opening of the divisions and at least 6 to 17 mm. smaller than the outer diameter of the stabilizing channel. The widths of the discharge space formed between the restrictors and the divisions may widen outwardly, advantageously to discharge chambers, from which said part of the liquid stream to be led olf is drawn off through tangential outlets. It is advantageous in this connection if the liquid drawn off is recirculated through a recirculating apparatus to the inlet openings. It is advantageous to provide the discharge space with baflies, particularly when viscous liquids are employed. When using two di'iierent liquids or for separate supply of gas and/or steam or also for separate discharge of the liquid, 21 further restrictor may be provided in the generator, the diameter of the central openings of the further restrictor being smaller than those of the divisions. Such further restrictors may be arranged at any position and in the required number in the generator.

The part of the stabilizing liquid which circulates between the different sections of the chamber is preferably circulated by means of a circulating device comprising for example a pump and if required a heat exchanger for cooling the circulating liquid.

The arrangement of the pair of electrodes, namely the inner and outer electrodes, and the arrangement of the reaction chambers for using the plasma ray produced is of known type, such as shown in copending application Ser. No. 42,809.

By the method according to the invention, a stabilizing channel of any length can be formed for a liquid vortex, an increased effect being produced at high voltage. The flow of liquid which is not drawn from the divided channel sections flows axially through the whole length of the stabilizing channel and should have as small of a flow as possible.

Experiments have shown that it is sufiicient for safe protection of the generator components of the channel against the effect of the arc discharge, and primarily against the intensive radiation from the arc column, to have a flow rate which is 2 to 10 times the amount of the plasma weight flowing out from the stabilizing chan nel. In known generator constructions this amount was 60 to 600 times the plasma weight. Attempts to employ smaller amounts of flow, e.g. by using mechanically rotating channel walls or porous channel walls, which could also be rotatable, have failed due to insufficient stability of the inner surface of the liquid channel. As a consequence of the friction on the walls and the restrictor, the speed of the liquid decreases too quickly. The speed of rotation required for satisfactory stability is too high to achieve mechanically.

The invention will be more readily understood from the following description of embodiments thereof given by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows a View in longitudinal section through a plasma generator with associated ducts and components illustrated diagrammatically;

FIG. 2A is a cross-sectional view taken substantially on line 2A-2A of FIG. 1;

FIG. 2B diagrammatically illustrates a modification of the regulation of the ducts of FIG. 1; and

FIGS. 3 to 8 respectively show broken-away views in longitudinal section of further modifications of the plasma generator of FIG. 1.

The stabilizing channel according to the invention is arranged in an electrode chamber having a pair of electrodes comprising an inner electrode 1 connected by a current supply conductor 5 to one terminal of a power source, and an outer electrode 1' connected to the other terminal of the power source. The high current electric arc discharge 13 is produced and maintained between the electrodes 1 and 1 as shown in FIG. 1. The electrode chamber is also provided with working liquid supply and discharge passages 20 and 21 which feed the working liquid to and from the spaces between restrictors 2, 3 and 4. The end of the channel adjacent the electrode 1 is limited by a restrictor 6. In the direction of the plasma beam flow, two restrictors 7 having central openings of smaller diameter than those of divisions 8, 8a, 8b and 10 are provided. Between these restrictors 7 gas or steam can be fed into the plasma ray 13 through inlet 18. In the space between the restrictors 7 and 6, working liquid is fed in through an inlet 19. This liquid is the same as that fed in through inlet 21 and is drawn off, after forming a liquid vortex, together with the liquid from the electrode chamber and any electrode burning products produced, through an outlet 20. Between the restrictor 7 and an outlet nozzle 12 there are arranged divisions 8, 8a, 8b and 10 for dividing the flow channel. In front of the two divisions 8a and 8b, restrictors 9 are provided which have a central opening of larger diameter than the divisions 8a and 8b. Between the discharge spaces formed by the divisions 8a, 8b and restrictors 9, which widen into collecting channels, a part of the stabilizing liquid stream is drawn off from the collecting channels through tangential outlets 17 and is recirculated or fed back by pumps 31 through heat exchangers 32 to the inlets 16 and is again fed tangentially into the channel to form a plurality of stabilizing liquid vortices around the plasma arc. The part of the liquid stream which flows axially through the whole channel to the outlet channel is fed in through inlet 18 controlled by flow regulators 24, and 33, 34. In the present case it is also possible to alter the stabilizing liquid supply through the flow regulators 29, and cocks 48, 49 after or before the pump 31. Between the division 10 and the restrictor 11 of the non-recirculated stabilizing liquid, together with the peripheral portion of the plasma gas and the cooling liquid which is fed in at inlet 14 for cooling the outlet nozzle 12, is drawn off through outlet 15. This liquid can be partially recirculated as cooling liquid via heat exchanger 32, pump and regulator back to inlet 14.

In FIG. 2B there is shown a modification of the regulation of the outlet 15 and supply ducts 14 and 18.

In FIG. 3 the end division 10 of FIG. 1 is replaced by a division 39 and an adjacent restrictor 9'. In this way there is effected in the front part of the channel a recirculation of part of the liquid beneath the inner surface of the liquid vortex. Recirculation is effected by means of a single pump 39. The supply and discharge ducts are provided with flow regulators 22, 23'.

FIG. 4 shows a further embodiment. In this case gas from inlet duct 21' flows through the inner electrode space. The cooled electrode 43 is connected coaxialiy with the channel. The stabilizing chamber, formed with divisions 8, 8a, 8b and restrictors 9, is connected to the cooled outlet nozzle 42 of the electrode chamber.

In FIG. 5 the stabilizing chamber channel is limited by the restrictor 54. The liquid from the stabilizing channel is drawn off between restrictors 6 and 54 through outlet 42. In this case a rotating cooled electrode 43' with a current supply conductor 44 is used as the inner electrode. The are discharge 13 ends at the surface of the electrode. The electrode chamber is supplied with working gas through inlets 45, 46 and the gas is drawn off together with a part of the plasma gas through outlet 47 and regulator 60. The regulator 60 is controlled by the varying pressure in the electrode chamber.

In FIGS. 6 and 7 hollow electrodes 61, 55, which may be rotatable are connected to the stabilizing channel. In the first case, the electrode chamber is closed at one end by the replaceable inner electrode element 62; electrode wear is combated by the replaceable element or material 62. The stabilizing liquid from the channel and the cooling liquid of the electrode are drawn off between restrictors 6 and 58. In the second case the electrode chamber is closed by wall 57'. The cooling liquid of the inner electrode and the cooling liquid for cooling the wall 57 are drawn off between the restrictors 56 and 62 together with a part of the plasma ray and any electrode products.

In FIG. 8 there is illustrated the possibility of connecting a plurality of stabilizing chambers axially in series. In this case electrode chambers are provided at both ends with inlets 21 and outlets 20. The discharge of the stabilizing liquid, which flows together on the surfaces of the divisions 10 and 10 in opposite directions from each two adjacent channels, is drawn off, with reaction products formed from the liquid by the plasma, through the space between the two divisions 1G and 10' and through the outlet 15.

I claim:

1. A plasma generator comprising a single electric power source, two electrodes connected to said single electric power source which is adapted to generate a high current electric arc therebetween, means connected between said electrodes to rapidly circulate liquid to form a plurality of liquid vortices around said electric are between said electrodes to constrict the arc, a plurality of first division means each arranged between two of said means to form liquid vortices, and each having a central opening having a first diameter, one source of stabilizing liquid, means connected to supply liquid from said one source of stabilizing liquid to the electric are adjacent to one of said electrodes, outlet means connected to lead oif liquid from at least one of said means to form liquid vortices spaced from said one electrode, at least one second division means having a central opening and defining with one of said first division means an annular outwardly spaced from the central openings, the central opening of said second division means having a diameter greater than the diameter of the opening of said first division means, said first and second division means are arranged coaxially with the liquid vortices formed by the means to form liquid vortices, a liquid cooler device, means connected with said annular chamber to lead ofi liquid therefrom and recirculate this liquid through said liquid cooler device and introduce it tangentially in front of said second division means into the liquid vortex contacting the second division means bounding said annular chamber, thereby maintaining the turbulent flow of this vortex.

2.. A plasma generator as set forth in claim 1, including at least one pair of third division means having central openings and connected coaxial with said first and 6 second division means and defining a second annular chamber, and means connected for supplying a fluid through said second annular chamber and the central opening of one of said third division means into the plasma of said high current electric arc.

3. An apparatus as set forth in claim 1 including another source of stabilizing liquid, and liquid conveying means connected to said another source of stabilizing liquid and operative to add liquid from said another source to the liquid being recirculated into the liquid vortex.

References Cited UNITED STATES PATENTS 9/1-959 Morton, Jr. 21912l P 9/1964 Giannini et a1. 313-231 X US. Cl. X.R.

2l9-12l P; 315-411 

